In recent years, as a mobile station represented by PHS (Personal Handy phone System), mobile phone system, and the like have become popular, it has been possible to make calls or obtain information anywhere and anytime. In particular, lately, as an amount of available information has shown steady growth, high speed and high quality wireless communication systems have been introduced in order to download a mass of data.
For example, as next generation PHS communication standards for high speed digital communication, ARIB (Association of Radio Industries and Business) STD T95 and PHS MoU (Memorandum of Understanding) have been proposed, and an OFDM (Orthogonal Frequency Division Multiplexing) scheme is used therefor. OFDM is one of multiplexing schemes. OFDM effectively uses a frequency band by using a plurality of carriers on a unit time axis and making phases of signal waves orthogonal between adjacent carriers to partially overlap bands of the carriers.
In addition, while OFDM assigns sub channels by time division to individual users, there have also been proposed OFDMA (Orthogonal Frequency Division Multiplexing Access) that allows a plurality of users to share all sub channels and assigns sub channels having the highest transmission efficiency to each user.
In ARIB STD T95 or PHS MoU, an modulation and coding scheme (hereinafter referred to as “MCS”) determined by adaptive modulation is transmitted to a transmitting device through an anchor channel in an FM-mode (Fast access channel based on Map-Mode) (for example, see Non-Patent Literature 1), and the transmitting device modulates data based on the MCS so that communication using optimum MCS under the communication environment at that time can be conducted.
Such adaptive modulation enables conducting stable wireless communication by: estimating communication environment between a transmitting device and a receiving device based on SINR (Signal to Interference and Noise Ratio) or a bit error rate of an uplink communication signal transmitted from a mobile station to a base station; and choosing MCS having higher modulation efficiency under better communication environment and MCS having low modulation efficiency under bad communication environment.
Moreover, in ARIB STD T95 or PHS MoU, in case where a receiving device receives incorrect data, an automatic repeat request (hereinafter referred to as “ARQ”) for requesting retransmission of the data is transmitted to the transmitting device that has transmitted the incorrect data. In response to such ARQ, the transmitting device performs retransmission of data to an MAC layer (low layer), so that the error can be effectively corrected for short control time (Non-Patent Literature 2). In addition, in ARIB STD T95 or PHS MoU, an HARQ (Hybrid ARQ) technique, which more improves packet error correction efficiency by combining such ARQ and FEC (Forward Error Correction), is also employed.
Non-Patent Literature 1: ARIB (Association of Radio Industries and Businesses) STD-T95
Non-Patent Literature 2: A-GN4.00-01-TS Rev. 3 “Next Generation PHS Specifications”, P331-340